11.2 Timer 2
Timer 2 is a 16-bit Timer/Counter which can operate either as a timer or an event counter, as selected by C/-T2
in the special function register T2CON. Timer 2 has four operating modes: Capture, Auto-Reload (up or down
counting), Baud Rate Generator and Programmable Clock-Out, which are selected by bits in the special function
registers T2CON and T2MOD, as shown below.
T2CON (Address=C8H, Timer/Counter 2 Control Register, Reset Value=0000,0000B)
7
6
5
4
3
2
1
0
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/-T2 CP/-RL2
TF2: Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2 will not be set when
either RCLK=1 or TCLK=1.
EXF2: Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and
EXEN2=1. When Timer 2 interrupt is enabled, EXF2=1 will cause the CPU to vector to the Timer 2 interrupt
routine. EXF2 must be cleared by software. EXF2 does not cause an interrupt in up/down counter mode
(DCEN=1).
RCLK: Receive clock control bit. When set, causes the serial port to use Timer 2 overflow pulses for its receive
clock in serial port Modes 1 and 3. RCLK=0 causes Timer 1 overflow to be used for the receive clock.
TCLK: Transmit clock control bit. When set, causes the serial port to use Timer 2 overflow pulses for its transmit
clock in serial port Modes 1 and 3. TCLK=0 causes Timer 1 overflows to be used for the transmit clock.
EXEN2: Timer 2 external enable bit. When set, allows a capture or reload to occur as a result of a negative
transition on T2EX if Timer 2 is not being used to clock the serial port. EXEN2=0 causes Timer 2 to ignore events
at T2EX.
TR2: Start/stop control for Timer 2. A logic 1 starts the timer.
C/-T2: Timer or counter select. When cleared, select internal timer. When set, select external event counter
(falling edge triggered).
CP/-RL2: Capture/Reload control bit. When set, captures will occur on negative transitions at T2EX if EXEN2=1.
When cleared, auto-reloads will occur either with Timer 2 overflows or negative transitions at T2EX when
EXEN2=1. When either RCLK=1 or TCLK=1, this bit is ignored and the timer is forced to auto-reload on Timer 2
overflow.
T2MOD (Address=C9H, Timer 2 Mode Control Register, Reset Value=xxxx,xx00B)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
T2OE
DCEN
T2OE: Timer 2 clock-out enable bit, set to enable and clear to disable.
DCEN: Timer 2 down-counting enable bit, set to enable and clear to disable.
Table 11-1. Timer 2 Operating Modes
RCLK + TCLK CP/-RL2
TR2
DCEN
T2OE
Mode
x
1
0
0
0
0
x
x
1
0
0
0
0
1
1
1
1
1
x
0
0
0
1
0
0
0
0
0
0
1
(Timer Off)
Baud-rate Generator
16-bit Capture
16-bit Auto-reload (counting-up only)
16-bit Auto-reload (counting-up or counting-down)
Programmable clock-out
45
MPC82G516A Data Sheet
MEGAWIN
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